Vacuum vessel for degassing molten metals

ABSTRACT

A vacuum vessel for degassing molten metals of the conventional kind comprising a steel jacket lined with refractory material with an intake pipe at its lower end for dipping into the melt to be degassed and a connection for connecting the vessel to a source of vacuum, is improved by providing a passage in the top of the vessel through which the vacuum connection communicates with the vessel, the passage being shaped so that it changes the direction of flow of gas from the vessel to the vacuum connection through at least 180*. Preferably the refractory lining merges at the top of the vessel into a neck which is surrounded by an annular chamber closed at the top by a cupola. The neck and the annular chamber form the passage and the vacuum connection communicates with one side of the annular chamber.

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority VACUUM VESSEL FOR DEGASSING MOLTENMETALS 8 Claims, 9 Drawing Figs.

US. Cl 266/34, 75/49 Int. Cl C21c 7/10 Field of Search 266/34 (V),

[ References Cited UNITED STATES PATENTS 3,027,150 3/1962 Harders 266/343,152,206 10/1964 Philbrick 266/39 Primary ExaminerCharles W. LanhamAssistant Examiner-John S. Brown Attorneys-Curt M. Avery, Arthur E.Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: A vacuum vessel for degassing moltenmetals of the conventional kind comprising a steel jacket lined withrefractory material with an intake pipe at its lower end for dippinginto the melt to be degassed and a connection for connecting the vesselto a source of vacuum, is improved by providing a passage in the top ofthe vessel through which the vacuum connection communicates with thevessel, the passage being shaped so that it changes the direction offlow of gas from the vessel to the vacuum connection through at least180. Preferably the refractory lining merges at the top of the vesselinto a neck which is surrounded by an annular chamber closed at the topby a cupola. The neck and the annular chamber form the passage and thevacuum connection communicates with one side of the annular chamber.

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Outstandingly successful in practice has been a method known as thevacuum lift method. The molten metal contained in a ladle is sucked upin successive portions by vacuum into the vacuum vessel through theintake pipe which extends downwards from the bottom of the vacuumvessel. Each portion is degassed in the vacuumvessel and, thendischarged again into the ladle. During the degassing process the vacuumvessel itself is repeatedly lifted and; lowered. Another already knownprocess is termed the vacuum circulation degassing process. For thisprocess the bottom of the vacuum vessel is equipped with two pipes whichdip into. the molten metal in a ladle. One of these two pipes is theintake pipeor riser, and theother is an outlet pipe or downcomer throughwhich the degassed metal is discharged back again into the pan. Themolten metal circulates constantly from the pan up through the riserinto the vacuum vessel and then back again through the downcomer intothe ladle, the melt being lifted up through the riser by the action of aconveying 'gas. This method has also been termed the gas lift process. 1

However, the already known vacuum vessels as described above have twomain disadvantages. In the firstplace there is a risk of spatteredparticles of molten metal reaching the vacuum connection, that is to saythe.,connection leading, to the source of vacuum, and then passingintothe vacuum pipe and even reaching the vacuum pump, a' highlyundesirable effect. A further disadvantage is the high rate of heat lossfrom the vacuum vessel. This occurs largely by radiation, mainly in theregion of the vacuum connection. Attempts have been made to interpose abaffle plate inside the vacuum vessel to 7 hold back the spatteredmetal. However it has been found that the baffle plate retains only thelargest particles of spattered metal, the smaller particles stillreaching the vacuum connection. Furthermore heat losses by radiation arein practice only slightly reduced by the effect of the baffle plate.

The object of the present invention is to remove these disadvantages,that is to say to provide a vacuum vessel the vacuum connection of whichis well screened from destructive influences emanating from the melt,the vacuum vessel at the same time providing a high degree of thermaleconomy.

To this end, according to this invention, in such a. vacuum vessel, thevacuum connection communicates with the vessel through a passage formedin thetop of the vessel which changes the direction of flow of 'gasfromthe vessel to the vacuum connection through at least 180.

The spattered metal particles cannot follow the change in direction andtherefore do not reach the vacuum connection. Furthermore radiated heatis intercepted before reaching the vacuum connection, which thereforeremains comparatively cool and the gas is aspirated at a high mass rateor flow.

In a preferred example of the invention the top of the vacuum vessel is'provided with a passage as follows. The upper part of the refractorylining merges into a neck, which is surrounded by an annular chamberclosed at the top by a eupola. The vacuum connection is in the side ofthe annular chamber and there is a through passage between the neck andWith regard to the detailed construction of the neck,,two-

advantageous alternatives are possible. In one example the neck is openat the top and: its top edge is situated above the LII top of the vacuumconnection but spaced below the undersurface of the cupola. The otherpossibility is to make the neck closed or substantially closed at thetop but with a side opening into the annular chamber at its side remotefrom the vacuum connection.

Vacuum vessels constructed in this wayshow a considerable improvement inthermal efficiency. However a great deal of heat is still lost duringthe pauses between two successive degassing. operations, the heatflowing through the neck of the vessel and over its top edgeto thevacuum connection. This disadvantage is remedied in thepreferred exampleof the invention by providing a movable closure between the neck and thesurrounding annular chamber. By closing this passage during the pausesbetween successive degassing operations the entire loss of heat fromthey interior of vessel to the vacuum connection is practicallyprevented. The heat is retained'in the vacuum vessel and the vacuumconnection is kept cool.

The closure between the neck. and the surrounding annularv chamber cantakevarious forms. If the neck is open at the top there can be a covermounted in the cupola in such a way that it can be lowered on to the topof the neck.

In order to ensure that the vacuum vessel iseasily accessible fromoutside, for cleaning or repairs, it is, preferable to connect a part ofthe cupola to the vacuum vessel in sucha way that the part can be openedup or moved out of the way. The part can be pivoted about a horizontalaxis on the steel jacket of the vessel. Y

Furthermore 'the vacuum vessel may be provided with a heating devicesituated below the neck, for example in the form. of an electric heatingrod, inorder to keep the temperature of the melt up to the desired valueduring the degassing process. However it is-a particular advantage ofthe invention. that the flow of extra heat which has to be supplied inthis way is comparatively small owing to the construction of the vacuumve'sselwith the; passage on its top.

Some examples of vacuum vessels constructed in accordance with theinvention are illustrated in the accompanyingdrawings in which: i

FIG. 1 is a vertical section through one example;

FIG. 2 is a cross section along the line 2-2 in FIG. 1;.

FIG. 3 is a vertical section, similar to FIG. 1 but of a second example;a

FIG. 4 is a partly sectional side view of the example shown in FIG. 1;

FIG. 5 is a verticalsection through example;

FIG. 6 is a verticalsection similar to FIG. 5, but of a fourth example;

FIG. 7 is a cross section along theline 7-7 in FIG. 6;

FIG. 8 is a vertical section similar to FIGS. 5 and 6, but of a fifthexample; and 7 FIG. 9 is a cross section along the line 9-9'in FIG. 8.

In the examplesillustrated the vacuum vessels are operated: by thevacuum lift method. In each FIG. the vessel as a whole has the indexnumerall. At the bottom of the vessel there is a single-intake pipe 2,which is made of refractory material and is capable of beingimmersed inthe molten metal contained in a ladle 3. Either the vessel 1 orthe-ladle 3 is vertically movable. The means for providing the verticalmovement are not a the upper part of a third part of the presentinvention. They are already known and are therefore not shown in thedrawing.

The vacuum vessel 1- has a steel jacket4 with a lining 5' ofrefractorymaterial, for example magnesite or alumina. The vacuum chamber 6, insidethe lining 5, is equipped with a horizontal heating rod 7 of carbon orsilica, situated a little; above the middle of the vacuum chamber 6.When the vessel is in operation an electric current flbws through theheating. rod 7. The vacuum chamber 6 also has at one side an inclinedbranchpipe 8,.projecting upwards. The branch pipe 8-.can-be used as aninspection opening, or for. feeding additives to the vacuum vessel;

The upper partiof the refractory lining S-merges into a-cylindrical neck9, which is surrounded by an-annular chamber 10*.

A vacuum connection 11 leading to a vacuum pump which is not shown inthe drawing, is connected to one side to the annular chamber 10.

The upper part of the annular chamber is covered by a cupola 12, whichis closed by a plate 13 capable of pivoting about a pivot 15 by means ofan arm 14, to which the plate is attached. The arrangement allows theplate 13 to be pivoted upwards and out of the way, as shown in FIG. 4,giving access to the vacuum chamber for cleaning and repairs. Throughthe plate 13, which is customarily clamped down on the top of the cupola12, a rod 17 slides in a bush l6.

Attached to the lower end of the rod 17 is a closure plate 18, linedwith a refractory material 19. As shown in FIG. 3 the closure plate 18can be lowered so that its lining 19 rests on the lip of the neck 9, bymeans of the sliding rod 17, so as to close the upper opening of thevacuum chamber 6.

FIG. 1 shows the vacuum vessel in its operating position. The moltenmetal is not shown. The chamber 6 is under vacuum and the molten metalit contains is being degassed. The gas released from the melt passesupwards through the neck 9 and so into the annular chamber 10, and fromhere is sucked away through the vacuum connection 11. The flowing gashas its direction changed several times on its path, so that most of thespattered metal impinges on the lining l9, and the remainder impinges onthe walls of the cupola 12. In this way it is ensured that the spatteredmetal does not reach the vacuum connection 11.

As soon as a vacuum operation has been completed, the melt is drainedout of the vacuum chamber 6, and the closure l8, 19 is closed so as toretain the heat stored in the vessel and prevent it from passing outthrough the vacuum connection 11 via the annular chamber 10. Undercertain circumstances it can be advisable to apply extra cooling to theannular chamber 10 and the vacuum connection 11. For this purpose theexample shown in FIG. 3 has cooling coils 21 and 22.

The example shown in FIG. 3 also has a further modification, in that thecupola has an internal lining 23 around the annular chamber 10.

The example shown in FIG. 5 also has a refractory lining 23 for theannular chamber 10. However in this case there is no movable closure forclosing the mouth of the neck 9.

In FIGS. 1 to 3 the neck 9 is surrounded by a steel jacket 24. Theexample of FIG. 5 also has this steel jacket, but between the neck 9 andthe steel jacket 24 there is a layer 25 of heat-insulating material,which can for example be fireclay of Superex. The insulating layer 25reduces the flow of heat from the wall of the neck 5 outwards throughthe annular chamber 10 to the vacuum connection 11.

In the example shown in FIGS. 6 and 7 the neck 9 extends upwards almostas far as the lower surface of the cupola 12, allowing very little spacefor the flow of gas over the upper lip of the neck 9 into the annularchamber 10. However the neck 9 has a side opening 26 on its side facingaway from the suction connection 11. In this way an even betterprotection is provided for the suction connection 11 against spatteredmetal. The gases sucked off pass along two different paths from the neck9 to the suction connection 11, most of the gas passing through the sideopening 26 and only a little over the upper lip of the neck 9.

In the example shown in FIGS. 8 and 9 the neck 9 extends all the way upas far as the lower surface of the cupola 12, allowing no flow of gasover the upper lip of the neck 9. All the aspirated gas leaves the neck9 through its side opening 26 which, as in the example of FIGS. 6 and 7,is situated in the side of the neck 9 furthest away from the vacuumconnection 11. In the example of FIGS. 8 and 9 there is a closure 27capable of closing the side opening 26. The closure 27 is mounted on asliding rod 28. The method of functioning is similar to that of theclosures of the examples shown in FIGS. 1, 3 and 4. In the example ofFIGS. 8 and 9 however the closure 27 moves in a radial direction withrespect to the axis of the vacuum vessel. The closure 27 of FIGS. 8 and9 and the closure l8, 19 of FIG. 1 both have the same purpose.

We claim: 1. In a vacuum vessel for degassing molten metals, said vesselincluding a steel jacket, a lining of refractory material in saidjacket, intake tube means at the bottom of said jacket for dipping intosaid.molten metal, and means defining a connection for connecting saidvessel to a source of vacuum, the improvement comprising means in thetop of said vessel defining a passage communicating said connection withsaid vessel, said passage being shaped to deflect the direction of flowof gas through at least between said vessel and said connection, saidpassage defining means comprising a neck formed at the top of saidrefractory lining, means defining an annular chamber surrounding saidneck, and a cupolaextending over said neck and said chamber, said vesselcommunicating with said neck and said connection communicating with oneside of said annular chamber, and further comprising means closing thetop of said neck and means defining an opening in one side of said neck,said one side being angularly spaced around said annular chamber fromsaid connection.

2. A vacuum vessel according to claim 1, further comprising a refractorylining in said annular chamber.

3. A vacuum vessel according to claim 1, further comprising a steeljacket surrounding said neck.

4. In a vacuum vessel for degassing molten metals, said vessel includinga steel jacket, a lining of refractory material in said jacket, intaketube means at the bottom of said jacket for dipping into said moltenmetal, and means defining a connection for connecting said vessel to asource of vacuum, the improvement comprising means in the top of saidvessel defining a passage communicating said connection with saidvessel, said passage being shaped to deflect the direction of flow ofgas through at least 180 between said vessel and said connection, saidpassage defining means comprising a neck formed at the top of saidrefractory lining, means defining an annular chamber surrounding saidneck, and a cupola extending over said neck and said chamber, saidvessel communicating with said neck and said connection communicatingwith one side of said annular chamber, and further comprising meansdefining an opening in the top of said neck, said opening being at alevel higher than said connection, but spaced below said cupola, and amovable closure between said neck and said annular chamber, and meansfor moving said closure to block said neck from said chamber. 7

5. A vacuum vessel according to claim 4, further comprising meansslidably mounting said closure in said cupola for lowering movement onto the top of said neck.

6. In a vacuum vessel for degassing molten metals, said vessel includinga steel jacket, a lining of refractory material in said jacket, intaketube means at the bottom of said jacket for dipping into said moltenmetal, and means defining a connection for connecting said vessel to asource of vacuum, the improvement comprising means in the top of saidvessel defining a passage communicating said connection with saidvessel, said passage being shaped to deflect the direction of flow ofgas through at least 180 between said vessel and said connection, saidpassage defining means comprising a neck formed at the top of saidrefractory lining-means defining an annular chamber surrounding saidneck, and a cupola extending over said neck and said chamber, saidvessel communicating with said neck and said connection communicatingwith one side of said annular chamber, and further comprising meansdetachably mounting a part of said cupola.

7. A vacuum vessel according to claim 6, wherein said part of saidcupola is a cover and said mounting means comprises means pivotallymounting said cover on said vessel for swinging movement about ahorizontal axis.

8. A vessel according to claim 1, further comprising heating means insaid vessel and means mounting said heating means below said neck.

1. In a vacuum vessel for degassing molten metals, said vessel includinga steel jacket, a lining of refractory material in said jacket, intaketube means at the bottom of said jacket for dipping into said moltenmetal, and means defining a connection for connecting said vessel to asource of vacuum, the improvement comprising means in the top of saidvessel defining a passage communicating said connection with saidvessel, said passage being shaped to deflect the direction of flow ofgas through at least 180* between said vessel and said connection, saidpassage defining means comprising a neck formed at the top of saidrefractory lining, means defining an annular chamber surrounding saidneck, and a cupola extending over said neck and said chamber, saidvessel communicating with said neck and said connection communicatingwith one side of said annular chamber, and further comprising meansclosing the top of said neck and means defining an opening in one sideof said neck, said one side being angularly spaced around said annularchamber from said connection.
 2. A vacuum vessel according to claim 1,further comprising a refractory lining in said annular chamber.
 3. Avacuum vessel according to claim 1, further comprising a steel jacketsurrounding said neck.
 4. In a vacuum vessel for degassing moltenmetals, said vessel including a steel jacket, a lining of refractorymaterial in said jacket, intake tube means at the bottom of said jacketfor dipping into said molten metal, and means defining a connection forconnecting said vessel to a source of vacuum, the improvement comprisingmeans in the top of said vessel defining a passage communicating saidconnection with said vessel, said passage being shaped to deflect thedirection of flow of gas through at least 180* between said vessel andsaid connection, said passage defining means comprising a neck formed atthe top of said refractory lining, means defining an annular chambersurrounding said neck, and a cupola extending over said neck and saidchamber, said vessel communicating with said neck and said connectioncommunicating with one side of said annular chamber, and furthercomprising means defining an opening in the top of said neck, saidopening being at a level higher than said connection, but spaced belowsaid cupola, and a movable closure between said neck and said annularchamber, and means for moving said closure to block said neck from saidchamber.
 5. A vacuum vessel according to claim 4, further comprisingmeans slidably mounting said closure in said cupola for loweringmovement on to the top of said neck.
 6. In a vacuum vessel for degassingmolten metals, said vessel including a steel jacket, a lining ofrefractory material in said jacket, intake tube means at the bottom ofsaid jacket for dipping into said molten metal, and means defining aconnection for connecting said vessel to a source of vacuum, theimprovement comprising means in the top of said vessel defining apassage communicating said connection with said vessel, said passagebeing shaped to deflect the direction of flow of gas through at least180* between said vessel and said connection, said passage definingmeans comprising a neck formed at the top of said refractory lining,means defining an annular chamber surrounding said neck, and a cupolaextending over said neck and said chamber, said vessel communicatingwith said neck and said connection communicating with one side of saidannular chamber, and further comprising means detachably mounting a partof said cupola.
 7. A vacuum vessel according to claim 6, wherein saidpart of said cupola is a cover and said mounting means comprises meanspivotally mounting said cover on said vessel for swinging movement abouta horizontal axis.
 8. A vessel according to claim 1, further comprisingheating means in said vessel and means mounting said heating means belowsaid neck.